Error on first use of tor

I used Tor browser bundle often on both linux and windows xp, now I'm at the end with my wits: I download Tor browser bundle as always, install it into a directory, start it. After the initial setup of my computer it worked ONCE, then I closed it, and whenever I try to start it again, and it says "Firefox is already running but not responding. To open a new window, you must first close the existing Firefox process, or restart your system".

I had the same problem on my old computer with Win XP, now I got a new one with Win7, the same thing. No firefox actually running (no such process in Task Manager), restarting doesn't help, simply impossible. I deleted the Tor directory, installed it again, doesn't work even once. Nothing.

I'm just an occasional user, going for one or two torrents once in a while, nothing serious. However, I'd prefer using Tor when doing this. If I only could get it running (installed and deleted and installed it, ect...???)